1. Field of the Invention
The present invention is related to a power-saving circuit and method for light sources of a liquid crystal display (hereafer called LCD), and more specifically to a power-saving circuit and method for controlling a driving circuit of a light source converter.
2. Description of the Prior Art
Commercial monitors are generally categorized into two types, cathode ray tube (hereafter called CRT) monitors and LCD monitors. The CRT monitor displays an image by accelerating electron beams to bombard phosphor powders coated on a screen Therefore, no external light source is required for the CRT monitor. On the other hand, the LCD monitor displays an image by utilizing side-light sources or backlight sources to illuminate liquid crystal molecules sandwiched between glass substrates and polarizing filters. Thus an extra light source is necessary for the display of the LCD monitors.
Generally speaking, the power consumption of the LCD monitors is lower than that of the CRT monitors. In addition, the LCD monitors have several advantages, such as light weight, small size and planarization, and so on. Therefore, the market share of the LCD monitors is gradually increasing. In a LCD monitor, the components that consume a majority of the power include the active matrix array composed of thin-film transistors (TFT) and the light sources and its driving circuit. As described above, the screen of the LCD monitor itself does not illuminate and the LCD monitor utilizes a sidelight source or a backlight source to illuminate the arranged liquid crystal molecules to produce images. Accordingly, the power consumption of the LCD monitor can be further reduced by saving the power consumed by the light source circuitry.
Therefore, the objective of the present invention is to provide a power-saving circuit and method for driving the light sources of a LCD monitor without sacrifying its visual effect.
The present invention achieves the above-indicated objects by providing a power-saving circuit for a light source of a monitor, such as an LCD monitor. The power-saving circuit indirectly controls the on-off state of the light source by controlling the the driving circuit of the light source. The power-saving circuit includes a control signal generator and a switching device. The control signal generator produces a low-frequency periodic control signal, the frequency of which is higher than a switching frequency of frames of the monitor. For example, the period of the control signal can be set as 10 msxcx9c20 ms. The switching device is coupled between the control signal generator and the driving circuit and used for alternatively controlling the on-off state of the light source by controlling the operation of the driving circuit.
In addition, there are two schemes for the switching device to control the driving circuit. In the first scheme, the switching device, which is coupled to the control signal generator, the power source and the power-in terminal of the driving circuit, alternatively enables and disables a power path between the power source and the power-in terminal of the driving circuit in response to the control signal from the control signal generator. For example, the power path can be grounded for cutting off the power supply. In the second scheme, the switching device, which is coupled to the control signal generator and the driving circuit, alternatively enables and disables the output of the driving signal from the driving circuit in response to the control signal from the control signal generator. For example, the driving signal can be disabled by bypassing.